The invention relates to a hot melt adhesive and coating composition processable by hot melt techniques and containing as the basic material predominantly amorphous poly-alpha-olefins.
It is known that it is possible to obtain, with hot melt adhesive compositions based on the poly-alpha-olefins utilized according to this invention and produced in a controlled fashion, an improved adhesion to substrates of various types by admixing (amount added 10-40% by weight) of a resin that is normally devoid of double bonds or contains a low amount of double bonds, such as, for example, a hydrocarbon resin, a terpene resin, or a hydrogenated colophony resin. However, besides exhibiting the advantage of improving adhesion, resins also display several disadvantages. They lower viscosity, i.e., cohesion, of the poly-alpha-olefin. Moreover, the resins usually combined with amorphous poly-alpha-olefins function as plasticizers in general and thus impair the heat deflection temperature thereof. Frequently, resins also lead to extensive impairment of heat stability, color, and odor of the melt-fluid compositions. Last, but not least, however, a significant improvement in adhesion by resin addition cannot be attained at all on certain substrates, such as polyolefins.
Also, the fact that functionalized polyolefins exhibit improved adhesion to polar and metallic surfaces and enhanced anchoring effect to fillers, such as, for example, calcium carbonate, has been basically known. However, this involves either high-molecular molding compositions containing, in part, nylon, rubber, or polyethylene, which are producible or processable only by way of expensive extruder techniques or hot melt formulations based on polyethylene or, alternatively, filler-containing compositions or compositions with a higher filler content, wherein the functional group exclusively serves the purpose of improving the anchoring of the polyolefins to a filler.
Therefore, the object to be attained resides in developing an optionally entirely resin-free, readily processable hot melt adhesive composition, making it possible to fully exploit during its processing the advantages of hot melt technology such as, for example, the lower outlay for apparatus as compared to the extrusion technique, the higher flexibility during the processing of a melt composition, for example, when changing the hot melt adhesive formulation, as well as the processing versatility (e.g., application by spraying), whereas this composition does not exhibit the drawbacks of the resin-containing formulations. Actually, various efforts have been undertaken in the past for effecting radical grafting of unsaturated carboxylic acids or their derivatives onto the poly-alpha-olefins used in accordance with this invention, in order to arrive at products having the above-enumerated advantages. Such efforts foundered, inter alia, on account on the very poor grafting yield and, respectively, on account of the facts that monomer can remain in the product, that radical grafting simultaneously initiates degradation or crosslinking reactions (for example, in case of poly-alpha-olefins containing ethylene), as well as that color impairment is brought about by the grafting reaction (see, for example, Minoura et al., J. Appl. Polym. Sci. 13, 1625 (1969); EP-OS 0 317 358; EP-OS 0 202 921; and EP-OS 0 269 000).